In the prior art, a hinge has played only a connection between a door and a framework thereof. The hinge is made separatedly from a shock-absorbing device which moves the door to be closed slowly and automatically and which is typically located on the upper portion of the door and connected between the door and the framework.
The shock-absorbing device is so complicated that trouble shooting thereof frequently takes place. And the device has to be installed only onto the upper portion of the door in a manner that the device is exposed out of the door. Therefore, in the shock-absorbing device of the prior art, there are problems in the installation on the restricted area, from an aesthetic point of view and high cost.
In order to solve the above problems, the inventor of the present invention disclosed Korean Patent No. 156093 which had been granted and entitled "HYDRAULIC AUTOMATIC SHOCK-ABSORBING HINGE" wherein the hinge has a piston on the end thereof and a cylinder having a reciprocating pipe therein. The piston has a switching valve and a check valve. A right-hand spiral groove and a left-hand spiral groove are formed opposedly with each other and on the reciprocating pipe.
A right-hand spiral cam is protruded on one side of the rotational shaft. And the right-hand spiral cam is engaged with the right-hand spiral groove and a bolt threadly engaged with the cylinder is inserted in the left-hand spiral groove to keep the balance under the movement of the cam in the upward or downward direction.
The hydraulic hinge having the construction mentioned above, has a good effect of shocking-absorbing. But when the right-hand spiral groove is moving upwardly or downwardly along the right-hand spiral groove such that buffering effect takes place by hydraulic pressure, the spiral cam applies a highly excessive load to the rotational shaft on the one side thereof, so that the shaft and the bolt engaged threadly with the cylinder may be broken out or cut out.